8186694: JShell: speed-up compilation by reusing compiler instances

Generalizing ReusableContext and using it in JShell to speed up processing.

Reviewed-by: mcimadamore, rfield

test/langtools/tools/javac/lambda/LambdaParserTest.java

@@ -246,9 +246,9 @@ public class LambdaParserTest extends ComboInstance<LambdaParserTest> {
 
     @Override
     public void doWork() throws IOException {
-        check(newCompilationTask()
+        newCompilationTask()
                 .withSourceFromTemplate(template)
-                .parse());
+                .parse(this::check);
     }
 
     void check(Result<?> res) {